This invention relates to highly absorbent and retentive materials for absorbing aqueous based fluids and more particularly for absorbing body fluids in such.products as sanitary napkins, diapers, bandages and the like. Specifically, this invention is related to compositions and methods for preparing crosslinked polyelectrolytes capable of absorbing and retaining many times their weight of such aqueous fluids.
Highly absorbent crosslinked polyelectrolytes and methods of preparing the same are already known. U.S. Pat. Nos. 3,669,103 and 3,670,731 teach use of these materials in diapers and dressings. U.S. Pat. Nos. 2,988,539; 3,393,168; 3,514,419 and 3,557,067 teach methods of making such absorbents and in particular are related to water swellable crosslinked carboxylic copolymers that are either crosslinked during copolymerization or crosslinked after polymerization and then neutralized to result in pendant ionic moieties capable of imparting water retention properties to the finished material. Additionally polyelectrolytes have been prepared which are cured or crosslinked employing epihalohydrine. For example, U.S. Pat. No. 3,980,663 employ epihalohydrines but has been found to be unacceptably slow and inefficient as a method for crosslinking such polymers.
In U.S. Pat. No. 4,076,673 an improvement in the rate and efficiency of curing polyelectrolytes has been accomplished by employing as a crosslinking agent a polyamidepolyamine epihalohydrine adduct of the kind commercially available from Hercules, Incorporated and sold by them under the Trademark Polycup.RTM.. A still further improvement in the choice of crosslinking agent is disclosed in U.S. Pat. No. 4,310,593 which teaches the use of monomeric amine epihalohydrine as a crosslinker which is said to have greater efficiency, longer shelf life and the convenience of being capable of shipping as a concentrate.
The above disclosures notwithstanding, there is still a need for improvement in crosslinked polyelectrolyte technology and in particular there is a need to improve the efficiency of the crosslinking reaction, the shelf life of the crosslinker and its convenience in use.